1. Field of the Invention
This invention generally relates to the shock-absorbing art and, more particularly, to a mechanical-impact type shock-absorbing assembly for a circuit interrupter which rapidly dissipates the kinetic energy of the movable contact and its operating mechanism during the opening stroke of the interrupter.
2. Description of the Prior Art
As is well known, power circuit interrupters or breakers generally comprise a pair of separable contacts that are operated within an enclosure which provides an insulating means (a vacuum, SF.sub.6 gas, oil, etc.) that efficiently extinguishes the arc generated when the contacts are forceably separated and then prevents the arc from restriking as the contacts continue to be rapidly opened until they are spaced a predetermined distance apart. The contact-opening operation, once triggered by a suitable signal means (manual or automatic) and trip mechanism, is completed in as short an interval of time as is mechanically possible in order to provide maximum protection to the power transmission line and associated equipment.
A major problem in the design of such power circuit breakers is the provision of suitable means for not only dissipating the kinetic energy of the movable contact and associated moving parts of the breaker during the contact-opening stroke but controlling the motion and rest positions of these components. The amount of override beyond the ideal rest position of the movable contact and the distance that the contact rebounds from such rest position, when the breaker is tripped, is determined by the mechanical, electrical and thermodynamic characteristics of the breaker and must not exceed certain limits if the breaker is to operate properly. Moreover, due to the large size and mass of the contacts and the related moving parts of the circuit interrupter, the severe mechanical strains improsed on the operating mechanism and associated stationary parts of the interrupter by the rapid deceleration of the moving contact and operating mechanism must be kept within safe limits to avoid excessive mechanical stressing of the operating components and support structure of the interrupter.
It is known in the prior art to use various kinds of shock absorbers to dissipate the kinetic energy of the moving parts of a circuit interrupter in a controlled fashion during the contact-opening operation. Such prior art shock absorbers were of the hydraulic, pneumatic, strain energy or friction type and, while generally satisfactory from a functional standpoint, they were rather complicated in construction and required periodic maintenance and inspection to insure that they were in good operating condition and properly adjusted. Moreover, they were not as cost-effective as the device described hereinafter.
An energy-absorbing stop assembly for an air-borne magnetic field detector which employs springs and a viscous damping liquid is disclosed in U.S. Pat. No. 3,674,251 (Tirabassi). Various other types of stop and shock-absorbing devices having resilient components are disclosed in U.S. Pat. Nos. 4,064,383 (Barkan); 4,267,419 (Maier et al.); and 4,491,709 (Chabot et al.).